Correcting the High Costs During the 1980'S massive U.S. government spending on development programs, such as the National Aero Space Plane programs (NASP) and Strategic Defense Initiative (SDI) have produced and tested light weight, re-usable structures able both to contain cryogenic propellants and withstand the heat of re-entry. The advanced materials these research programs have brought about are ideally suited to SSTO rockets. Since empty weight drives development, production, and operating costs on both air and space systems the potential for even greater cost reduction should increase as SSTO rocket technology and operations mature. Graphite epoxy, aluminum lithium, titanium metal matrix composites, and aluminum honeycomb panels are now off the shelf materials available to build propellant tanks and space structures. This has all but solved the earlier SSTO weight problems. By designing for reliability, safety, a minimum of support personnel, and an economical flight rate the SSTO transport will be more like a commercial aircraft than a space booster. Conventional boosters normally now operate with reliabilities of 94% to 96%. The SSTO transports, using multiple levels of back up capabilities to provide intact abort, and including escape-ejection mechanisms for catastrophic failure, should have 99.9% reliability. These safety features also allow progressive flight testing like aircraft, thus increasing reliability and reducing redundancy requirements as well as maintenance and inspection costs. Unlike ELV's which throw away everything on each flight, or even Shuttles which toss off tanks and other parts, the SSTO's only expendables will be fuel and propellants used for control along with life support expendables if needed. When one adds to this flight rates of once or twice weekly that spread fixed costs over large numbers of flights substantial cost reduction over conventional launchers are achievable. There appear to be no insurmountable problems in devising engines to meet the SSTO requirements. More than adequate progress has been made in rocket engine thrust to weight ratio in recent years. The problem has been the configurations best suited to meet the abort specifications. Current proposals envision engines that can be easily maintained and are structurally efficient. When these are clustered in groups of up to ten modules, each with self contained pumps, combusters, and nozzles, they will provide the necessary redundancy for safe operations, engine out capabilities, and ease of engine change. Modifications to existing engine designs appear to be adequate to demonstrate the first SSTO's even though improved engines made specifically for SSTO operations, will no doubt be built for use in operational systems. All engines will be liquid fueled. Most proposals plan to use inexpensive H2-O2 although other fuels are being examined. Rocket powered ships designed to either complete their mission or be brought back safely in the event of engine failures have not as yet been successfully demonstrated. The ability to do this today is, however, more one of configuration
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